This invention relates to an engine with a supercharger and more particularly to an improved induction and fuel feed system for a supercharged engine.
The use of superchargers is well known to increase the performance of an engine of given engine displacement. Superchargers, particularly those of the centrifugal type, do not provide any significant boost to the intake charge at low engine speeds. The effect of the supercharger is more pronounced at higher engine speeds. Furthermore, when accelerating from low engine speeds, the supercharger, particularly those of the centrifugal and tubrocharged type, tend to lag in acceleration relative to the degree of throttle opening. Thus, at low speeds and under such low speed accelerating conditions, the supercharger may actually reduce rather than increase the engine performance. It has, therefore, been proposed to provide a bypass around the supercharger which is valved in such a way so as to permit air to enter the induction system without flowing across the supercharger at low speeds and when the engine is not developing significant boost.
It is also known that it is desirable to limit the maximum boost generated by the supercharger. If excessive induction system pressure is provided as a result of the supercharger, the engine may have a tendency to preignite and/or be overloaded and fail. Therefore, it has also been proposed to provide a pressure relief valve on the outlet side of the supercharger that will limit maximum pressure. If, however, the over pressure is relieved to the atmosphere and the engine is of the injected type, the air flow meter will sense a greater air flow than has actually existed and provide an overly rich fuel discharge at times when the pressure relief valve is open. If, on the other hand, the engine is of the carbureted type, the fuel air mixture may be discharged to the atmosphere through the pressure relief valve resulting in obvious fuel wastage as well as possible safety hazards. It has, therefore, been further proposed to provide a separate passage which can be used to return the excess pressure back to the intake side of the compressor. Of course, such an arrangement obviously complicates the piping associated with the engine.
It is, therefore, a first principal object of this invention to provide an improved induction system for a supercharged engine including a supercharger bypass and a pressure relief system.
It is a further object of this invention to provide an induction system for a supercharged engine wherein the bypass around the supercharger is also employed as the means for relieving excess pressure in the induction system.
As has been noted above, when fuel injection is employed it is desirable to maintain the accurate fuel air ratio by controlling the amount of fuel discharged in relation to the total air flow. In many instances, however, the pressure in the induction system at the point of fuel discharge can vary significantly and thus alter the amount of fuel discharged by the fuel injection nozzle. This is particularly true in conjunction with supercharged engines. With such engines, when the supercharger is developing a high degree of boost the fuel injection nozzle will have to discharge into a higher pressure area than under conditions of low boost. This can cause the engine to run unduly lean under high boost conditions with the resultant damage.
It is, therefore, a further object of this invention to provide an improved fuel injection system for an internal combustion engine.
It is another object of the invention to provide an improved fuel injection system for a supercharged internal combustion engine.
As has been discussed, even supercharged engines are not particularly efficient in their running at low engine speeds. This is one of the reasons it has been proposed to provide a bypass around the supercharger through which the intake air may flow at low speeds and under acceleration from low speed. Even when such bypasses are employed, however, the engine, like a normally aspirated engine, is not particularly efficient under these running conditions. One reason for the inefficiency at low speeds is the fact that the intake charge is delivered to the chambers at an extremely slow velocity. This has a tendency to cause fuel condensation resulting in the necessity of providing overly rich mixtures and the extremely slow flame propagation which occurs in the combustion chamber.
It is, therefore, a still further principal object of this invention to provide an improved efficiency induction system for a supercharged internal combustion engine.
It is another object of the invention to provide an induction system for a supercharged engine that offers improved effficiency and running characteristics at low engine speeds.